We thank Dr Elkind for his interest in our recent article on RPLS.1 Reversible posterior leukoencephalopathy syndrome represents many clinical entities, including eclampsia, calcineurin inhibitor toxic effects, and hypertensive encephalopathy, that are now unified under a single moniker owing to recognition of the shared clinicoradiologic appearance. Unfortunately, the underlying patholophysiology is not well understood. Schwartz et al2 suggested that hyperperfusion is associated with dysfunction in cerebral autoregulation, with resultant increased capillary permeability and leakage. The opposing theory, less widely accepted, suggests that RPLS lesions are the result of hypoperfusion and presumed ischemia. Dr Elkind noted a recent series reporting decreased blood volume in RPLS lesions on magnetic resonance imaging perfusion coupled with a high rate of vasculopathy and also noted that RPLS occurs in 9% of patients with reversible cerebral vasoconstriction syndrome.3,4 Although this supports the hypoperfusion theory, the presence of vasculopathy is incongruous with many other reports of RPLS as well as routine clinical observation results. Furthermore, there are reports demonstrating hyperperfusion on single-photon emission computed tomography in RPLS as well.2,5 In our series, cerebral angiograms were normal in 2 patients. An additional 10 patients had magnetic resonance angiograms of the head, of which 8 showed widely patent vessels. The 2 abnormalities seen on magnetic resonance angiograms included a right vertebral artery occlusion at the level of the skull base and upper neck (case 15) and a small-caliber vertebrobasilar system with a truncated left posterior cerebral artery (case 18), both with residual T2 hyperintensity lesions in the supratentorial subcortical white matter remote from the territories of the abnormal arteries. The fact that we did not find vasculopathy to be common in our series of patients with RPLS favors the hyperperfusion theory. Neuroimaging findings on magnetic resonance imaging, although distinctive for RPLS, are not absolute and radiographic mimics such as cerebral angiitis can occur6; thus, caution should be used in interpreting data from series of patients with RPLS where follow-up neuroimaging is not obtained. Variability in results may also occur owing to dynamic changes and timing of neuroimaging.
Lee VH, Wijdicks EFM, Manno EM, Rabinstein AA. Reversible Posterior Leukoencephalopathy Syndrome—Reply. Arch Neurol. 2008;65(8):1135-1137. doi:10.1001/archneur.65.8.1136-a